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How to change signal between A and B w/o cutting the wire?

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david90

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Is this possible?

I have a signal that comes out of A and into B. A and B are connected by a wire. Is There a way to modify or change the signal that go from A to B wihtout cutting the wire?
 

Re: Is this possible?

by placing it in magnetic field maybe
 

Re: Is this possible?

Place another cable in paralel whith the A to B cable. Then feed the 2nd cable with the desired signal. If crostalk between those wires is high, the signal in the 2nd cable will appear in the A to B cable. This will work better for high frequency signals and no-insolated cables.
 

Re: Is this possible?

What you want to modify in your signal? Is it shape, amplitude or what?
 

Is this possible?

If the wire between A and B is struck by lightning, I'm pretty sure the signal will change.
 

Is this possible?

I have a photointerupter and it is sending out pulses with respect to speed of a scooter. The photointerrupter is soldered to the PCB. what i'm trying to do is allow the pulse signal between 0-1khz pass but impede it if greater than 1khz and I don't want to cut any traces on the PCB. What is the best way to do it? Will the parallel method above work?
 

Is this possible?

the parallel method is for signals at much higher frequencies. you can probably just solder a simple R and C at one end for a simple RC filter. or if you need more selectivity, then insert a generic IC filter.
 

Re: Is this possible?

Looks like you want to override the speed limit of the motorcycle; anway let's get the task.
Just one question: when the frequency is beyond 1 KHz, you just don't want any signal or you want that the frequency will remain at 1 KHz ?

In the first case a low pass filter is enough, in the second case is more complicated because you have to substitute the incoming signal witha 1KHz fixed frequency.
The way how to add the signal to the circuit depends on the circuit, if you don't want any solderingthe task can be reached with a spring pressing on the connector pin or something similar.
Anyway, have you any schematic abot the existing circuit ?

Mandi
 

Is this possible?

after 1khz, the signal could remain at 1khz or completely blocked (0hz).

How would I connect the RC filter to the circuit? Basically, A is sending a signal to B thru a trace on PCB. Somehow i need to pull the input of B to ground (0hz) when A is sending out a signal at 1khz.

I need to refresh my network analysis skill.
 

Is this possible?

You can put a pull up resistor with a supply source, this may change your signal, without cutting the wire.
 

Is this possible?

You can try simply putting a capacitor to GND or supply anywhere along the path. This provides a short to higher frequencies, however you need to know the resistance going into node A/B in order to know what value capacitor to put.
 

Is this possible?

what if the resistance going into node A/B doesn't have a resistance?

If I use a cap to short circuit, wouldn't that be bad to node A which sends out the signal?
 

Is this possible?

Node A and B does have a resistance.
If node A or B is a low impedance driver, then you're in trouble and the cap won't work. A low impedance driver is pretty much like a voltage source which good luck filtering out without the use of series components.

If Node A and B have a high impedance, then the problem may become that the capacitor needs to be too small, or the high impedance varies too much. Then you may need to add a series resistor with the capacitor (the combined unit connected in parallel to A or B).

A cap is bad to node A (the transmitter I'm assuming) because it loads it down, but the loading is more predominant at higher frequencies. This is how it filters the higher frequencies out.

Greg
 

Is this possible?

you could rectify the signals from A, put a large capacitor at the output of the rectifier and get a DC bias proportional to the signal Frequency. When this bias rasises above a specified level (it shall as the frequency rises) ground the point.

Well... This may cause a bias to appear and vanish creating a very dynamic situation. Don't know if it might solve your purpose.

Can anyone explain any defects in this?
 

Is this possible?

The defects are as follows:

1) Most signals have more then 1 frequency in it. Don't want to loose all data on it, just some select frequencies.

2) All frequencies get rectified. Putting a capacitor on the output of the rectifier does not "select" the frequencies, but increases the averaging period. Therefore very low frequencies will look like ripples, high frequencies will look more like a constant DC signal. The DC value for all of them will be the same, except the lower frequencies will have a ripple riding on top of the DC. This ripple will probably trigger any detector after.

3) Since we are not "breaking" the line, a detector that grounds the output will also hence ground the input. You will then loose all signals coming into the rectifier, causing the DC voltage to drop, releasing the "Detector" which causes the DC voltage to rise again. In effect, we got oscillation....

This will suffice for now.

Greg
 

Is this possible?

Okay, I agree with point 3. I had forseen it.

A schmitt's trigger could solve point 2.

But if I have got the question correct, the signal of 1Khz seems the only signal comming. If it a square wave...as it most probably is, it shall have harmonics. The higher order harmonics shall be very small and shall not affect point 2.

I guess the optical inerrupter is near the wheels as in case of a computer mouse... And the siganl is something like FM of a digital signal.

So it is of little consequence if everything is lost. Or is it?
 

Is this possible?

great inputs. THe original question leads to this project that i'm doing and is a little trouble. It is related to node A and B. Node A is a photointerrupter and node B is just whatever that
processes the pulses made by the electric motor.
 

Re: Is this possible?

connect using capacitor to allow only the AC value
connect using inductor to allow only the DC value
connect using parallel LC circuit to allow a particular frequency
 

Re: Is this possible?

hi

yes it is possible in high frequency.

in high freq. a lot of things may be effect in a system.

NTFS.
 

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